The present invention relates to the field of synchronous hierarchy data transport networks and, more precisely, to a method and device for improving the flexibility and transparency in the high-speed frame transport at the nodes of synchronous digital hierarchy networks.
The need to increase the transport capability and the functional potentiality and therefore the flexibility of the synchronous hierarchy (SDH or SONET) networks but, at the same time, to keep down additional costs created by these higher requirements, is more and more stringent.
As it is known, e.g. from ITU-T Recommendation G.707, the synchronous hierarchy high-bit rate signal frame at STM-N level comprises a header section hereinafter called xe2x80x9coverheadxe2x80x9d, and a payload section, formed by the so called virtual containers VC-N, hereinafter referred as xe2x80x9cpayloadxe2x80x9d. The overhead section, in turn, comprises a section called xe2x80x9cregeneration sectionxe2x80x9d, RSOH, and a section called xe2x80x9cmultiplex sectionxe2x80x9d, MSOH. Said sections are known and reference is made e.g. to said Recommendation for a detailed explanation of their structure and use.
It is known that the transport is carried out through the payload section whereby the continuity and the transparency at the network nodes is provided, and that can thus be passed through the nodes in the high-speed lines without being processed, while the RSOH and MSOH sections are used for other network functions and are terminated at the nodes themselves, i.e. they are read out in order to process them (to get e.g. performance measures or error rates relating to them) and they are re-written before being put again in the outgoing STM-N frames. It will be appreciated that such reading, processing, and rewriting operations may be referred in a more general sense as termination-type local reprocessing operations or, more simply, as local reprocessing operations.
A drawback, which is however observed, is that the transport capability based on the payload section of the frame may result to be insufficient for some needs.
Therefore, it is a first object of the present invention to overcome said drawback and to provide a method for providing the full transport continuity and transparency in the high-speed nodes of the network, according to which, in addition to the payload section, also the MSOH section, and further at least partially the RSOH section, are used; i.e. the MSOH section, and also part of the RSOH section, are passed through in the node points along with the payload without terminating them, also providing the full networking functionality, i.e. the capability of carrying out the OAMandP (operation, administration, maintenance and provisioning) functions of the transport network.
The network nodes supporting such new functionalities could be implemented through the use of known devices such as optical dividers, hereinafter called optical cross-connects, and WDM-type (Wavelength Division Multiplex) line systems.
The use of said optical cross-connects is however a very expensive solution, with a technology which is not consolidated and repeatable with enough reliability yet. Moreover, it is not possible to provide and measure the quality of transmitted service in terms of BER (Bit Error Rate).
Furthermore, in order to transmit the resulting SDH frames over the related optical wavelengths, it would be necessary to add further overhead information on said wavelengths, and this would be a further design complication.
Therefore, a further object of the present invention is to overcome the aforesaid drawbacks and to provide a novel device for implementing points of flexibility at the nodes of the synchronous hierarchy transport network using a digital divider, hereinafter called MS-DXC (Multiplex Section Digital Cross Connect), and SDH or WDM terminals for mere transport requirement. Both the MSOH and possibly the RSOH overhead sections are handled by the digital cross connect in a manner equivalent to the payload section, thus providing the transparency for the payload and for the MSOH section, as well as, potentially, for the RSOH section.
Therefore, in accordance with the present invention, a high-capacity network node comprises known high-capacity WDM and SDH terminals and a multiplex section digital cross-connect, MS-DXC, which connects the low-speed interfaces of said terminals and which allows the realisation of the distribution and grooming functions for local and pass-through traffic so that the traffic granularity handled by the node is in terms of SDH STM-N synchronous hierarchy sections and not lower, or PDH plesiochronous hierarchy e.g. at a bit rate of 565 or 140 Mb/s and not lower.
Hence, a further point of flexibility for the network using the RSOH frame section is implemented by means of a digital MS cross-connect for providing all the OAMandP functionalities, i.e. operation, administration, maintenance and provisioning functionalities, of the transport network that transmits the payload and the MSOH section in a transparent way.
In this way most of the, or also the whole, STM-N frame can be handled by higher network levels connected to the high-speed node.
In order to achieve such objects, the present invention provides a method and device for improving the flexibility, the transparency and the management in the high-speed frame transport at the nodes of a synchronous digital hierarchy network, as better described in the claims which form an integral part of the present description.
Further objects and advantages of the present invention will result in being clear from the following detailed description of an embodiment thereof and from the accompanying drawings attached merely by way of a non limiting example.